before you paste the link, flick the light switch thing in the top left corner of the reply box. It wasn't working for me either until I did that, something to do with the board automatically putting tags around the link or something idk

Browser? Also, post your CODE if you want to give me the slightest chance to help you guys. If it's Chrome, apparently Chrome thinks it does a good thing by changing up links that you paste into a rich-text-editor (like the one Invision board has) - so if you're on Chrome you might have to post embeds in plain text (light switch, as someone wrote earlier). Or get a better browser.